Failure to install cryptography wheels for Python 3.6

[asavaritayal]

Since the Azure SDK takes a dependency on Cryptography which is a native package, publishing a Python Function App fails asking the user to publish using --build-native-deps.

This shouldn't be the case since Cryptography does provide version 3.6 compatible wheels, see here - pyca/cryptography#4382

/cc @maiqbal11 @elprans

[ankitkumarr]

@asavaritayal, I looked into this. Cryptography provides whl for python 34 abi3. Looks like we do something similar to pip download --platform manylinux1_x86_64 --python-version 36 --abi cp36m. There's two issues here-

1. pip download seems to specifically look for 36 version file even though the 34 file seems to be supported for 3.4+.
2. I don't know much about Python abis. According to https://github.com/pypa/pip/issues/6070`, abi3 is compatible cp36m, but pip does not know so.

We can get around 2 by doing pip download twice with --abi abi3 and --abi cp<version>m. But, I am not sure if we can do anything about 1. Given that we need to specify the python version and I don't think there's a way of knowing in advance which version file (34 here) we need to download.

[asavaritayal]

Adding @zooba and @1st1 to see if they have a recommendation on this one.

[zooba]

Nope, this looks like a pip limitation that requires their issue 6070 to be fixed. I just experimented with a few variations and none will choose the cryptography wheel unless you specify --python-version 34.

I don't have a recommendation right now other than to engage the projects and see what help we can provide. I'll ping both of them.

As a workaround, you could do this (tested separately but these commands need checking):

pip download --platform manylinux1_x86_64 --python-version 34 --abi abi3 cryptography --dest wheelhouse
mv wheelhouse/cryptography-2.6.1-cp34-abi3-manylinux1_x86_64.whl wheelhouse/cryptography-2.6.1-cp36.cp37-abi3.cp36m.cp37m-manylinux1_x86_64.whl
pip download --platform manylinux1_x86_64 --python-version 36 --abi cp36m --find-links wheelhouse -r requirements.txt

Renaming the cryptography wheel to include the ABI that you're going to download for in the name (dot separators let you specify multiple compatible versions) and using --find-links will avoid trying to download it again, though it will copy the wheel from wheelhouse to wherever the output of the second command is going.

[ankitkumarr]

Thanks @zooba for the workaround and pinging the projects.

This issue comes up when we try and download wheels from user's requirements.txt. Even with that workaround, we would have to specify --python-version 34. The problem is- we would not know which version to specify for a given package from requirements.txt as I assume this problem is not exclusive to cryptography.

Unless, you are aware of a way to figure out which wheel version would satisfy a given python version. So, figuring out that we need cp34 wheel for cryptography if we want to download the wheel for version 36?

[zooba]

Nope, no way to figure that out. Which is why I said a temporary workaround is to special case cryptography (and presumably any others that we hear about).

[ahmedelnably]

Blocked on pip getting updated

[kshyju]

@vrdmr Is this still a valid issue? Can you advice what the action item here should be?

[microsoft-github-policy-service]

This issue has been automatically marked as stale because it has been marked as requiring author feedback but has not had any activity for 4 days. It will be closed if no further activity occurs within 3 days of this comment.

If you are not the original author (asavaritayal) and believe this issue is not stale, please comment with /bot not-stale and I will not close it.